Investments (Proceeds from Sales of Securities and Realized Gains and Losses) (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
|
| Investments [Abstract] | ||||
| Proceeds | $ 0 | $ 18,191 | $ 18,530 | $ 43,782 |
| Realized gains | 0 | 273 | 52 | 688 |
| Realized losses | $ 27 | $ 41 | $ 96 | $ 229 |